This project is designed to identify structural features of mammalian mRNA that may be concerned with the control of its function in the cytoplasm, and to study the processes that control the translation of mRNAs for specialized proteins in differentiated cells. Interactions between specific polynucleotide sequences and proteins or other components will be characterized, and these interactions will be compared in the mRNA of polysomes and of free messenger ribonucleoprotein particles. The purification of mRNPs and the development of an assay system for these particles will be attempted. The isolation of mRNAs and mRNPs specific for mouse myeloma immunoglobulin and rat liver albumin will be carried out and any special structural features will be identified. The distribution of these mRNAs in active and inactive state in the cytoplasm will be determined in cells in different physiological states. Factors specific for the translation of these specialized mRNAs will be investigated.